Individuals who suffer from multiple endocrine neoplasia type 2 (MEN-2) are afflicted with a variety of tumors, including pheochromocytomas and medullary thyroid carcinomas, which arise from derivatives of the primordial neural crest. Understanding the regulation of neural crest differentiation is critical because these progenitor cells give rise to a wide variety of cell types whose abnormal differentiation underlies many human diseases. The ultimate goal of this proposal is to understand the biological function of NGFI-A, a zinc finger transcription factor that is rapidly, but transiently, synthesized in pheochromocytoma cells treated with nerve growth factor. Defects in NGFI-A function may result in abnormal differentiation or proliferation, as aberrant expression and activity of other transcription factors have been closely linked to defects in development and initiation of neoplasia. Interestingly, NGFI-A suppresses colony formation when introduced into a variety of cell types, including many derived from the neural crest. This property, shared by many tumor suppressor genes, will be examined by determining whether it is a consequence of growth arrest or cell death. Clearly NGFI-A regulates gene expression, but whether it is capable of both promotion and repression of transcription will be determined by delineating the domains critical for these activities. Full appreciation of the biological role(s) of NGFI-A awaits the identification of NGFI-A-regulated genes. These genes will be isolated by purifying DNA fragments to which NGFI-A binds in vivo using chromatin immunoprecipitation. NGFI-A is a member of a family of closely related transcription factors which could potentially attenuate or antagonize NGFI-A activity. This will be explored by determining whether some or all family members recognize the same nucleotide sequence(s) recognized by NGFI-A. Finally, to assess the in vivo function of NGFI-A, homologous recombination in embryonic stem cells will be used to create transgenic mice with loss-of-function mutations in the NGFI-A gene. Since NGFI-A may promote differentiation and/or suppress cell growth, this NGFI-A "knockout" mutation will provide an invaluable tool for studying the contribution of NGFI-A to the regulation of tissue and organ formation and the development of neoplasia.